Midland District was one of four districts of the Province of Quebec created in 1788 in the western reaches of the Montreal District and partitioned in 1791 to create the new colony of Upper Canada. Known as Mecklenburg District (named after the castle Mikilenburg in the Mecklenburg region of Germany) until 1792, it was abolished in 1849. The district town was in Kingston.
The district was originally bounded to the east by a line running north from the mouth of the Gananoque River and to the west by a line running north from the mouth of the Trent River. The district town was Kingston. In 1798, the district was reorganized to consist of the counties of:
In 1831, Prince Edward County was separated to form Prince Edward District. In 1837, Hastings County was split off to form Victoria District.
In 1849, the district was replaced by Frontenac and Lennox and Addington counties.